Joe Biden was Vice-President from January 2009 thru January 2017. The role of any Vice-President is to privately offer the President their opinions and advice and to publicly support the President's policies. A Vice-President can advise on policy, but does not decide policy.
President Obama not only welcomed a variety of differing and dissenting opinions, he encouraged them. It has been well documented and widely reported that Biden privately presented Obama with a strong dissent to the advice of military leaders for surging a large number of troops into Afghanistan in an attempt to restructure the country. Ultimately, Obama did not take Biden's advice and surged first 20,000 and then an additional 30,000 troops into Afghanistan until there were about 100,000 US troops there. In policy meetings and discussions, Biden was a constant thorn in the side of Obama's military advisors and consistently argued that it would not achieve the goals that were promised; that there was no winnable war in the region for the US; and that the focus should be on counterterrorism efforts. He was ultimately proven right.
The policy approach to Afghanistan, and more broadly in Iraq and Syria, that Biden proposed then privately, and since then publicly, was a narrowly focused mission of counterterrorism with enough specialized forces on the ground to monitor and combat, with the assistance of local fighters, any terrorist organizations like Al-Qaeda or ISIS. He vocally opposed, then and now, the ideas that large numbers of US troops were necessary or that we were capable of reforming or remaking the region to our liking. He also opposed then, and opposes now, bringing US forces on the ground down to zero as he believes that we need eyes and ears and forces on the ground to enable the US to maintain our own security against potential threats.
While Biden throughout his career has shown that he is willing and able to admit to, and learn from, mistakes and errors in judgement and a willingness to change his mind based on past experience and new information, his position in this area has been fairly consistent for over a decade. As a Senator, he opposed the troop surge in Iraq in 2007 by Bush and argued for retaining residual forces there in 2011 as Obama's VP. None of this is a secret. Since leaving office as VP, numerous books, opinion pieces, and news articles by people inside and outside of the Obama administration have reported his positions and advice to the President in addition to his own public statements.
Biden has had plenty of critics on this position over the years from the left and right, and from within and outside of the Obama administration. Open debate and criticism is healthy in a democracy. It's also quite easy to fabricate false or misleading narratives that obscure the truth. The truth is that Biden has for years opposed large numbers of troops and troop surges regardless of who was President. He was a dissident voice in the Obama administration for troop surges in Afghanistan and withdrawing from Iraq without a residual force remaining for security. He opposes Trump's plan to bring troop levels down to zero and that is consistent with his long standing positions.
It is also true that the Taliban want all US forces out of Afghanistan and eagerly support Trump for his statements that he intends to remove all US forces quickly. It's not a smear to report that fact. It's called journalism.